Why Heat Is a Problem
As electronics get faster, heat generated per unit area rises with them. Left uncontrolled, heat causes:
- Throttling — APs and CPUs deliberately lower their clock speed when temperature hits the limit.
- Display degradation — heat conducted into an OLED panel causes image retention, color shift and shorter panel life.
- Shorter component life — batteries and electrolytic components degrade dramatically faster at high temperature.
- Safety and reliability — for automotive electronics operating long hours in hot environments, thermal design is reliability.
Heat Moves in Three Ways
Thermal design starts from the three heat-transfer mechanisms: conduction, convection and radiation. In fanless products — smartphones, tablets, automotive modules — you cannot count on convection, so the key question becomes how fast and how widely you can spread heat by conduction.
The Heat Spreading Approach
If the heat of a small source (hotspot) stays put, that one spot overheats. A heat spreading sheet (Thermal Spread Sheet/Tape) uses a highly conductive layer such as Cu (copper) to spread heat rapidly in the lateral direction, lowering the saturation (peak) temperature and preventing heat from concentrating into specific components.
Applied over AP chips, DDIs and OLED heat zones, a Cu Thermal Spread Sheet disperses heat widely to lower the saturation temperature and blocks conduction into the OLED panel. The Cu layer is highly conductive, so it doubles as an EMI shield for noise from the main board's AP chip, and it can be integrated with foam tape — heat spreading, shielding and cushioning in a single part.
Key Metric: Thermal Conductivity (W/mK)
Thermal conductivity indicates how well a material transfers heat. For reference: air is about 0.03, common plastics 0.2–0.5, aluminum about 200 and copper about 400 W/mK. When reading a datasheet, check two things:
- Direction (X-Y vs. Z axis) — for heat spreading, the lateral (X-Y) conductivity is what matters. If a datasheet does not state the direction, be sure to confirm it.
- Balance with thickness — the same material carries different total heat depending on thickness; optimize within the available design space.
Copper (Cu) vs. Graphite: Heat Spreading Materials Compared
The two dominant materials for heat spreading sheets are copper and graphite. Neither is universally "better" — the right choice depends on the required performance and assembly conditions.
| Copper (Cu) sheet | Graphite sheet | |
|---|---|---|
| Thermal conductivity | About 400 W/mK, uniform in all directions (isotropic) | Hundreds to over 1,000 W/mK in-plane, low through-thickness (anisotropic) |
| Strengths | Doubles as an EMI shield, good mechanical strength and processability, usable for grounding | Light and thin with outstanding in-plane spreading |
| Watch out for | Heavier, and in-plane spreading is lower than graphite | Brittle (needs a protective layer), conductive dust must be managed, limited shielding capability |
In practice, Cu-based sheets go where EMI shielding is also needed, graphite goes where extreme in-plane spreading is required, and many designs combine the two. Detailed specifications of our thermal products are on the Thermal Solution page.
Thermal Material Selection Checklist
- Identify the heat source's location, size, power and the allowable temperature.
- Decide where the heat should go (chassis, cover, cooler zones).
- Choose high X-Y conductivity for spreading, or Z-axis performance for layer-to-layer transfer.
- Check whether combined functions (EMI shielding, cushioning) are needed — fewer parts means less thickness and cost.
- Confirm adhesion and die-cutting processability for production.
FAQ
- How many degrees can a heat spreading sheet save?
- It varies widely with heat load, applied area and the escape path, so there is no universal number. Hotspot mitigation (saturation temperature reduction) is a reliable effect, and we can verify it with thermal analysis and measurements under your actual set conditions.
- Can one material handle both EMI shielding and heat dissipation?
- Yes. Cu-based heat spreading sheets provide shielding by themselves, and combining conductive tape with thermal spread tape above an IC chip to suppress noise and reduce saturation temperature simultaneously is a widely used design.
Need to solve heat and EMI with one material design?
Tell us your application conditions and we will propose the optimal thermal and shielding solution.
